feat: support custom git config

[shaug]

This allows for, among other things, relying on git URL mappings, which can normalize protocols:

git config --global url."ssh://git@github.com".insteadOf "https://github.com"

Or add credentials from environment variables for a CI tool:

git config --global \
    url."https://${USERNAME}:${PASSWORD}@github.com/${OWNER}/".insteadOf \
    "https://github.com/${OWNER}/"

I have a project relying on this change and it is working spendidly.

[pgrzesik]

Hey @shaug - thanks a lot for the proposal, overall it makes sense 👍 There are failing checks in CI though (prettier-related it seems), could you please take a look into that?

[shaug]

Thanks, @pgrzesik. The code has been prettified.

[pgrzesik]

Hey @shaug - unfortunately it seems like the tests are failing as well - if you'd be able to take a look it will be much appreciated 🙇